All of the major implant manufacturers over the last couple of years have introduced line extensions to their total knee replacements that tout high-flex knee replacement. Most of these designs have incorporated features that will allow increased flexion of the femoral component (the part that covers the end of the thigh bone) with the tibial component (the part that covers the top of the shin bone). There are several factors that influence the amount of range of motion in knee replacement. These include the amount of motion present prior to surgery, the girth and size of the leg, and the degree of arthritis. For the overwhelming majority of activities of daily living, knee flexion in the range of 115° to 120° is adequate. There are certain cultural, religious, and other factors that require knee flexion in excess of this. For patients with excellent range of motion prior to surgery, a high-flex knee design can accommodate more range of motion as long as the patient is capable of obtaining that range of motion. It should be pointed out that the amount of motion that is present in a knee when it is being tested with the patient lying on a table and passively bending the knee is quite different then the amount of motion the knee can obtain with an active deep knee bend.
The majority of patients today are well served by the standard knee replacement and it will allow them to obtain the amount of motion that their knee can achieve. For a subset of patients noted above, high-flex knee can be of use and you should speak to your orthopedic surgeon about the pluses and minuses of these designs.
